The strong growth in demand for portable consumer electronics is driving the need for high-capacity storage devices. Non-volatile semiconductor memory devices, such as flash memory storage cards, are becoming widely used to meet the ever-growing demands on digital information storage and exchange. Their portability, versatility and rugged design, along with their high reliability and large capacity, have made such memory devices ideal for use in a wide variety of electronic devices, including for example digital cameras, digital music players, video game consoles, PDAs and cellular telephones.
Cross-sectional side, top and bottom views of a conventional semiconductor package 20 are shown in FIGS. 1 and 2A and 2B, respectively. (molding compound has been omitted from FIG. 2A). Referring initially to FIGS. 1 and 2A, conventional packages include a plurality of semiconductor die, such as flash memory die 22 and controller die 24, affixed to a substrate 26. A plurality of die bond pads 28 may be formed on the semiconductor die 22, 24 during the die fabrication process. Similarly, a plurality of contact pads 30 may be formed on the substrate 26. Memory die 22 may be affixed to the substrate 26, and then controller die 24 may be mounted on die 22. All die may then be electrically coupled to the substrate by affixing bond wires 32 between respective die bond pad 28 and contact pad 30 pairs. The substrate may include a copper layer etched into electrical leads for transmitting signals and data to and from the die 22 and 28. Once all electrical connections are made, the die and bond wires may be encapsulated in a molding compound 34 to seal the package and protect the die and bond wires.
The controller die 24 is generally smaller than the memory die 22. Accordingly, the controller die 24 is conventionally placed at the top of the memory die stack. In FIGS. 1 and 2A, the die bond pads 28 of memory die 22 all bond out to a single, side edge of the substrate 26. The controller die bond wires 32 are shown bonded between bond pads 28a and a separate row of contact pads 30 along the same edge. The controller die 24 is also wire bonded between a second row of die bonds pads 28b along an adjacent edge of the controller die 24 and a second row of contact pads 30.
Referring now to the bottom view of FIG. 2B, the package 20 may be a land grid array (LGA) package including a plurality of contact fingers 40 etched into the copper layer on the back side of the substrate. The fingers 40 allow the package 20 to be removably used within a slot of a host device. A plurality of test pads 42 are also defined in the copper film on the back side of the substrate 26 to allow electrical test and debug of the package upon completion. The test pads 42 are typically covered up once the electrical test is completed. The number of contact fingers 40 and test pads 42 shown in FIG. 2B is by way of example and may vary. Vias (not shown) are formed through the substrate 26 to allow electrical connection of the die through the substrate to the contact fingers 40 and test pads 42.
In testing finished semiconductor packages, there will be some number of packages that fail due to a problem with the controller die in the package. Instead of throwing away the entire package, it is known to “reclaim” the package by electrically isolating the controller die 24 within the package and repackaging the memory die in a new semiconductor package. Today, the controller die 24 is electrically isolated from the substrate 26 by mechanically grinding off the molding compound 34 on the top of the package 20 until the wires 32 connecting the controller die 24 to the substrate 26 are exposed and severed. The grinding equipment is typically either custom designed or is a non-standard piece of semiconductor equipment used in the machining shop with very low units per hour. Regardless of the equipment, the grinding is carried out in an uncontrolled environment and does not provide adequate grinding depth control.
Mechanical grinding also introduces mechanical stresses on the memory die 22, which may crack or otherwise damage one or more of the memory die 22. The grinding also reduces the original package thickness, which weakens the package structure and complicates downstream surface mount technology (SMT) processes due to non-standard package thickness. The grinding process may also expose the passive components in the package (not shown), which have a vertical height above the substrate 26 approaching that of the controller die bond wires 32.